I have just tried it on windows it works like a charm now nice work and thanks digerati1338 and chrisjs162216!
Edit: It seems to install both bootloaders (kind of)if you hold down the left/back/reverse button it will boot into the sansa firmware like it does with the normal bootloader has the boot screen and everything all though its probably expected to happen. If started and left untouched it will still boot into the orignal firmware like it is supposed too and it boots into rockbox fine when the select button is held.

Yes, I changed the button from left to select since it is easier to use. Thus, pressing any other button (left, right, up, down, whatever) will not change anything.